Many different methods for the preparation of epoxides have been developed. Generally, epoxides are formed by the reaction of an olefin with an oxidizing agent in the presence of a catalyst. The production of propylene oxide from propylene and an organic hydroperoxide, such as ethyl benzene hydroperoxide or tert-butyl hydroperoxide, is commercially practiced technology. This process is performed in the presence of a solubilized molybdenum catalyst, see U.S. Pat. No. 3,351,635, or a heterogeneous titania on silica catalyst, see U.S. Pat. No. 4,367,342. Another commercially practiced technology is the direct epoxidation of ethylene to ethylene oxide by reaction with oxygen over a silver catalyst.
Much current research is conducted in the direct epoxidation of olefins with oxygen and hydrogen. For example, JP 4-352771 discloses the formation of propylene oxide from propylene, oxygen, and hydrogen using a catalyst containing a Group VIII metal such as palladium on a crystalline titanosilicate. The Group VIII metal is believed to promote the reaction of oxygen and hydrogen to form an in situ oxidizing agent. U.S. Pat. No. 5,859,265 discloses a catalyst in which a platinum metal, selected from Ru, Rh, Pd, Os, Ir and Pt, is supported on a titanium or vanadium silicalite. Other direct epoxidation catalyst examples include gold supported on titanosilicates, see for example PCT Intl. Appl. WO 98/00413.
Besides oxygen and alkyl hydroperoxides, another oxidizing agent useful for the preparation of epoxides is hydrogen peroxide. U.S. Pat. No. 4,833,260, for example, discloses olefin epoxidation using hydrogen peroxide and a titanium silicate zeolite. The preferred solvent for this reaction is water due to the cost and availability of aqueous hydrogen peroxide. However, the reaction in water proceeds at low rates and a co-solvent is necessary to give sufficient productivity to epoxide. Clerici, et al., J. Catal. (1991) 129, 159, for example, teach that a water concentration above 50 weight percent considerably decreases the rate of reaction in propylene epoxidation. The Clerici article also teaches that methanol is considered the best solvent for the epoxidation of propylene. Thus, one distinct disadvantage of olefin epoxidation with hydrogen peroxide by titanium zeolites is the need for expensive co-solvents. This requirement results in additional expense for olefin epoxidation processes using hydrogen peroxide.
In sum, new processes that would allow the aqueous epoxidation of olefins using hydrogen peroxide are needed. Particularly valuable processes would result in increased productivity to epoxide.